Wireless, you can actually use a PSP to operate your PS3 so long as both are connected to an internect connection - some one in Australia that's been linked up with your PS3 can turn it on and off, and play certain games like Lair...trippy stuff.
Internet is free if you're by an unsecure wireless router - but like Aqua said - it's hard to type on and is more of a novelty addition.
The PS3 games are supposed to incorporate using the PSP in games, though - like it's going to become the rear view mirror in Grand Turismo, and you can literally play through Lair on it.